I hope you are using this code in single.php from where the whole of the post is displayed. For displaying the links (Next/Prev), you need to check the function.

get_template_part()
in the same file (Single.php of your theme). In my case function in single.php has been passes parameters like
<?php get_template_part( 'content-single', get_post_format() ); ?>
So, you will open the "content-single.php" according to the parameters specified in the function and paste the same code
<div class="alignleftfp">
<?php next_post('%', '<img class="imgalign" src="' . get_bloginfo('template_directory') . '/images/1.png" alt="Next" /> ', 'no');
?>
</div>